The invention relates to a switching arrangement for the control of an adjustable member, such as a valve, whereby the adjustable member is turned off or closed automatically after an adjustable time period during which the adjustable member was on or opened. The invention particularly relates to the control of a valve which forms part of an automatic sprinkling system.
Experience has shown that watering of a garden or lawn is most successful whenever the sprinkling is carried out at the onset of twilight. Consequently very many gardens are sprinkled at this time, so that the pressure in the water mains fluctuates with a relatively high degree of variation from the normally encountered pressure. If automatic sprinkling is carried out at this time, the success of watering, which is difficult to estimate in advance, would tend to be irregular.
In prior art automatic sprinkling systems a water control clock mechanism is used to control the sprinklers. The clock mechanism closes an adjustable valve in series connection with a water sprinkler after the course of a manually initiated valve open period set on the clock mechanism. Automatic opening of the valve is not possible with this arrangement, so that it cannot be used whenever a water sprinkler is to be turned on and off daily, for several days.
Furthermore, this type of prior art control for water sprinkling systems operates with a precision clock mechanism, which is sealed against the water carrying parts of the arrangement. This sealing requires a considerable construction expenditure.
An electric time switching clock is available on the market by means of which an electric circuit may be turned on and off daily at certain times during a 24 hour period. The times of turning on and off may be adjusted successively. However, the use of such an electric switching clock to overcome the difficulties mentioned above with respect to twilight watering is prohibitive, as it would represent an unnecessary expense due to the cost of the clock mechanism and moreover may be adjusted for a time dependent upon twilight only after special considerations, calculations, and adjusting efforts.